//
//  Stepper.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 12/01/2016.
//  Copyright 2016 Thomas Harte. All rights reserved.
//

#pragma once

#include <cstdint>

namespace SignalProcessing {

/*!
	Allows a repeating action running at an input rate to determine how many times it should
	trigger an action that runs at an unrelated output rate; therefore it allows something with one
	clock to sample something with another.

	Uses a Bresenham-like error term internally for full-integral storage with no drift.

	Pegs the beginning of both clocks to the time at which the stepper is created. So e.g. a stepper
	that converts from an input clock of 1200 to an output clock of 2 will first fire on cycle 600.
*/
class Stepper {
public:
	/*!
		Establishes a stepper with a one-to-one conversion rate.
	*/
	Stepper() : Stepper(1,1) {}

	/*!
		Establishes a stepper that will receive steps at the @c input_rate and dictate the number
		of steps that should be taken at the @c output_rate.
	*/
	Stepper(uint64_t output_rate, uint64_t input_rate) :
		accumulated_error_(-(int64_t(input_rate) << 1)),
		input_rate_(input_rate),
		output_rate_(output_rate),
		whole_step_(output_rate / input_rate),
		adjustment_up_(int64_t(output_rate % input_rate) << 1),
		adjustment_down_(int64_t(input_rate) << 1) {}

	/*!
		Advances one step at the input rate.

		@returns the number of output steps.
	*/
	inline uint64_t step() {
		uint64_t update = whole_step_;
		accumulated_error_ += adjustment_up_;
		if(accumulated_error_ > 0) {
			update++;
			accumulated_error_ -= adjustment_down_;
		}
		return update;
	}

	/*!
		Advances by @c number_of_steps steps at the input rate.

		@returns the number of output steps.
	*/
	inline uint64_t step(uint64_t number_of_steps) {
		uint64_t update = whole_step_ * number_of_steps;
		accumulated_error_ += adjustment_up_ * int64_t(number_of_steps);
		if(accumulated_error_ > 0) {
			update += 1 + uint64_t(accumulated_error_ / adjustment_down_);
			accumulated_error_ = (accumulated_error_ % adjustment_down_) - adjustment_down_;
		}
		return update;
	}

	/*!
		@returns the output rate.
	*/
	inline uint64_t get_output_rate() const {
		return output_rate_;
	}

	/*!
		@returns the input rate.
	*/
	inline uint64_t get_input_rate() const {
		return input_rate_;
	}

private:
	int64_t accumulated_error_;
	uint64_t input_rate_, output_rate_;
	uint64_t whole_step_;
	int64_t adjustment_up_, adjustment_down_;
};

}
